Some medication, such as insulin, is typically self-administered using a medical delivery device such as an injection pen. The typical diabetes patient will require injections of insulin several times during the course of a week or a day. However, typical injection devices do not address the problem of a user not remembering when the last injection was administered.
Even shortly after administering a dose of insulin, the user now and then will be in doubt as to whether he actually carried out an injection or not. This could be after minutes or even hours after the intended time for performing an administration. Thus, there exist the potential hazard that the patient chooses not to take his medication or that he takes it twice.
Some prior art devices, such as the electronic syringe disclosed in WO 97/30742, are provided with an electronic monitoring system adapted to automatically start an electronic timer when a selected dose is injected and to show the progress in time on an electronic display. Such an injection device generally provides a satisfactorily solution to the problem addressed above. However, for simpler devices such as disposable injection devices, i.e. the so-called pre-filled devices, the solution with integrated electronics will in most cases not be economically viable. In addition, such a solution may not be environmentally acceptable due to the potential increase in the disposal of electronic components such as batteries etc.
WO 99/43283 include disclosure of a timer device which is intended to be used with pre-filled injection pens, where the timer device is configured for releasable attachment to the pre-filled pen so that the timer device can be removed from a pen once it is ready for disposal and be attached to a new pen. The timer device is configured to detect when an injection is performed and to communicate this via indicator lights that remains turned on for a certain time period from the administration of the dose.
WO 02/064196 includes disclosure of a related timer device, however being more sophisticated in respect of the features it provides.
Although disclosing environmentally acceptable solutions, both the devices of WO 99/43283 and WO 02/64196 offer somewhat complex solutions which require additional operational measures from the user before they can be used. In addition, the device of WO 99/43283 offers a rather bulky design in that it is attached to the rear housing of an injection pen so as to surround it and further requires a second part which couples to the injection button of the device to monitor the movements of the injection button.
In a further reference, U.S. Pat. No. 6,620,133 includes disclosure of a mechanical delay switch equipped injection or infusion device where an acoustical or vibrational signal is emitted when a time delay of 5 to 10 seconds has elapsed after the injection movement has ended to alert the patient to remove the canula from the skin. Further, in U.S. Pat. No. 6,236,624, a mechanical timing device is disclosed which includes a fluid operated timing device which is used for controlling the operation of a further device.